Aircraft primers and paints are among the most difficult paints to strip. An aircraft is stripped every 5 to 10 years for aesthetic reasons, and also in order to reveal possible faults in the aircraft structure. Aircraft paints are often highly crosslinked two-component paints. High-altitude flying amplifies this initial crosslinking by the UV radiation emitted by the sun. This produces areas which are more crosslinked than others depending on their degree of UV exposure. It is common, for these areas, to add stripper and to leave it to act for longer. An aircraft is stripped by spraying it with a thickened stripper which must not run down vertical walls.
The stripper is left to act for a certain period (rarely less than one hour in the case of stripping aircraft), and is then rinsed off with a jet of pressurized water. The flakes and shreds of paint are then carried away by the water through a grille into a catch pit. After settling in the catch pit, the sludge is incinerated and the liquid phase is distilled.
For environmental and toxicity reasons, it is currently sought to replace aircraft strippers based on methylene chloride and/or phenol (Ind. Finish 45(10) 1969, 28-31). These two compounds have proven to be very effective at stripping aircraft, especially in the presence of an acidic or alkaline activator, but they pollute the environment. In order to strip aircraft primers and paints (of the polyurethane, epoxy and alkyd type), it is necessary to use a very effective solvent base. The development of aqueous formulations containing a solvent fraction is particularly advantageous in order to limit the environmental and toxicity problems. It will thus be sought to incorporate as much water as possible into the formulations and to limit the contents of toxic products.
For this application, effective formulations based on benzyl alcohol have already been developed. These are water/benzyl alcohol emulsions activated with an acid or a base. American patent U.S. Pat. No. 5,405,548 describes a mixture based on benzyl alcohol, water and formic acid for stripping aircraft. According to the authors, the efficacy of their stripper is due to the "benzyl formate" ester formed in situ in the course of formulation, that is to say during mixing between the benzyl alcohol and the formic acid. Benzyl formate is thought to be the active compound and, on account of its cost, it is much more advantageous to synthesize it during the formulation operation than to introduce it as a constituent.